1. Field of the Invention
This invention relates to protection of ruminants from the effects of stress, particularly those involving an outbreak of virulence of Pasteurella haemolytica. Pasteurella haemolytica is a gram-negative bacterium that inhabits the upper respiratory tract of ruminants. During periods of stress, the organism enters into a virulent stage and proliferates in the respiratory tract. There, it may be inhaled into the lungs, inducing a disease called pneumonic pasteurellosis or shipping fever of cattle. All U.S. cattle, sheep, and goats are susceptible. There are 16 serotypes of P. haemolytica based on chemical differences in the outer capsular polysaccharide. P. haemolytica serotype Al is the primary cause of pneumonic pasteurellosis in cattle. The resulting pneumonia is costly to the producer and difficult to treat. Some animals die. In cattle alone, shipping fever accounts for an estimated loss of three billion dollars worldwide of which $500 million dollars is from the United States.
2. Description of Prior Art
Many veterinary products are available that contain P. haemolytica but their effectiveness in preventing pneumonic pasteurellosis is questionable. Resistance to experimentally induced pneumonic pasteurellosis can be enhanced by vaccination with live P. haemolytica, but not with formalin-killed P. haemolytica, P. haemolytica leukotoxin or P. haemolytica lipopolysaccharide. In fact, it is not uncommon for some animals vaccinated with live vaccines to have complications or animals with formalin-killed vaccines to have more severe lesions than nonvaccinated animals. This applies also to the poorly immunogenic capsular polysaccharide of P. haemolytica serotype Al which is composed of N-acetylaminomannuronic acid and N-acetylmannosamine.